The word “mussel” derives from musculus, which is the diminutive of mus, the Latin word for a mouse. This is not such a bad description of M. margaritifera.

Its decline parallels that of its host. In the last forty years of the eighteenth century pearls were exported from Scotland to Paris to the value of £100,000, an immense sum in today’s terms. (Round pearls, the size of a pea, in perfect condition, were worth up to £4 each.) The meat of the mussel is reported to have been used as bait in the Aberdeen cod fishery but this may be an error for the common mussel. Thankfully the market for freshwater pearls was killed off by the opening up of trade with the East and with the islands of the Pacific, from which far finer pearls could be obtained.

The decline of the salmon is referred to elsewhere. But it may be noted here, to give an idea of the number of gills to which M. margaritifera could attach itself, that in July 1743 no less than 2,560 salmon were taken in a single haul of the net at the Cruives Pool on Beat One of the Thurso river. (John Horne, The County of Caithness, 1903)

FRESHWATER PEARL MUSSELS

The relationship between the freshwater pearl mussel (Margaritifera margaritifera) and the salmon is curious and, to the former, crucial, for during its larval stage the mussel is attached to the gills of its salmonid host. It then drops off to grow to adulthood in riverbed gravel. It doesn’t reproduce until at least the age of twelve and can live for a century. It is now rare. The sites where it is known to exist are heavily protected.

Such is the gravity of the situation that in 2012 SNH and what was then called RAFTS combined with other environmental bodies to launch a project called “Pearls in Peril” with the aim of restoring habitat and raising awareness of pearl mussel conservation.

Distribution of Special Areas of Conservation (SACs) of Margaritifera margaritifera.